1. Field of the Invention
The present invention generally relates to computers, and more particularly to a method of installing a computer operating system on one of a variety of hardware platforms. The method involves loading of a dynamic boot filesystem prior to loading of the computer operating system (boot image), and then retrieving the dynamic boot filesystem during installation of the operating system.
2. Description of the Prior Art
The basic structure of a conventional computer system 10 is shown in FIG. 1. The heart of computer system 10 is a central processing unit (CPU) or processor 12 which is connected to several peripheral devices, including input/output (I/O) devices 14 (such as a display monitor and keyboard) for the user interface, a permanent memory device 16 (such as a hard disk or floppy diskette) for storing the computer's operating system and user programs, and a temporary memory device 18 (such as random access memory or RAM) that is used by processor 12 to carry out program instructions. Processor 12 communicates with the peripheral devices by various means, including a bus 20 or a direct channel 22. Computer system 10 may have many additional components which are not shown, such as serial and parallel ports for connection to, e.g., modems or printers. Those skilled in the art will further appreciate that there are other components that might be used in conjunction with those shown in the block diagram of FIG. 1; for example, a display adapter connected to processor 12 might be used to control a video display monitor.
Computer system 10 also includes firmware 24 whose primary purpose is to seek out and load an operating system from one of the peripherals (usually permanent memory device 16) whenever the computer is first turned on. The process of seeking out and loading the operating system is referred to as "booting" the computer. Computer system 10 may be designed to allow firmware 24 to re-initialize an operating system without turning the computer off and back on again (a "soft" boot). Firmware 24 is essentially a series of machine instructions which are typically stored in a read only storage (ROS) device, such as read only memory (ROM). As shown in the flow chart of FIG. 2, after power to computer system 10 is turned on (26), processor 12 begins to execute the firmware instructions and seeks out an operating system (28). If an operating system is found, it is loaded (30) into temporary memory 18. Thereafter, the operating system allows other application layers to be added, i.e., user software programs (32). The boot sequence is essentially steps 28 and 30. In this manner, a given computer hardware construction can be adapted to run a variety of operating systems.
The foregoing description generally applies to any type of operating system, including two popular operating systems known as MSDOS and UNIX (MSDOS is a trademark of Microsoft Corp.; UNIX is a trademark of UNIX System Laboratories), but the present invention has particular application to UNIX. UNIX is a multi-user, multi-tasking operating system which is available from a variety of sources with different versions. These include, among others, System V (American Telephone & Telegraph), AIX (International Business Machines) and Mach (NeXT Computers). FIG. 3 illustrates a typical boot image 34 that is loaded as a UNIX operating system. Boot image 34 includes a base kernel portion 36 and a boot filesystem portion 38. Kernel 36 acts as the intermediary between user programs and hardware devices, and includes, among other things, device drivers. Boot filesystem 38 is the RAM-based file system that provides user commands to manipulate computer objects, such as files, directories and symbolic links. Boot filesystem 38 can also contain loadable device drivers and other platform-specific loadable kernel extensions. When firmware 24 sees boot image 34 (such as on a floppy diskette, hard disk or CD-ROM disk), it transfers control to that operating system (kernel 36) after loading boot image 34.
A given operating system can be adapted to run on various types of hardware platforms. With some operating systems, such as MSDOS, the operating system is fairly independent of the hardware platform, i.e., a given copy of the MSDOS operating system can be used to boot computers manufactured by many sources, since the hardware architecture and BIOS (basic input and output system) functions remain constant from manufacturer to manufacturer. Other operating systems, like UNIX, are less portable due to significant differences between the various types of hardware that have been designed to run UNIX. In this regard, boot filesystem 38 includes information that is hardware dependent, such as the PAL (Portability Assist Layer, or Platform Abstraction Layer), which contains the specific instructions for communicating with the particular hardware devices of a given manufacturer.
This hardware dependence makes marketing of the operating system more difficult since different versions must generally be provided for each UNIX workstation manufacturer. One prior art method of overcoming this difficulty is to provide multiple PALs (one for each manufacturer), i.e., multiple boot filesystems as indicated at 40, 42. Alternatively, a single, huge boot filesystem could be provided, containing support for multiple platforms. While these approaches allow a single boot image to be distributed for use with any workstation, they are undesirable in that the boot image is much larger than necessary (because it contains all the unused PALs) and so takes up more system resources. They also fail to accommodate new hardware platforms, i.e., those that are designed after the release of the operating system. It would, therefore, be desirable to provide an operating system which is easily loaded on different hardware platforms without requiring multiple RAM-based boot filesystems, and it would be further advantageous if the method of installing the operating system allowed for simple incorporation of new hardware platforms.